Add a parameter to optionally not close loop on exit
Add a parameter to optionally not close loop on exit

The issue here is that some clients, like me, may have other cleanup
they need to do to gracefully shut down other coroutines outside of the
aiohttp server request handler coroutines. Because run_app closes the
loop those coroutines that are running the same loop but are outside of
aiohttp's control will immediately emit ugly stack traces because they
are attempting to continue operating on a closed loop.

By adding a parameter that controls closing the loop clients like me can
simply disable closing the loop and do our own additional cleanup before
closing the loop ourselves

KeepSafe/aiohttp,rutsky/aiohttp,rutsky/aiohttp,pfreixes/aiohttp,Eyepea/aiohttp,playpauseandstop/aiohttp,rutsky/aiohttp,hellysmile/aiohttp,arthurdarcet/aiohttp,KeepSafe/aiohttp,arthurdarcet/aiohttp,pfreixes/aiohttp,arthurdarcet/aiohttp,KeepSafe/aiohttp,hellysmile/aiohttp